Correlation Versus Causation

According to a study of the nearly 140,000 women who were enrolled in the Women’s Health Initiative, women who breast-fed their babies had a lower risk of developing heart disease and diabetes later in life than women who did not breast-feed their babies. The headline of the New York Times article about the research read “Breast-Feeding Benefits Mothers, Study Finds”. Is this a correct summary of the research?

The answer is “NO”! This is a classic case of the common misunderstanding about the relationship between correlation and causation. Yes, there is a clear correlation between breast-feeding and a lower risk of diabetes and heart disease later in life, according to the study. But that is not proof that the act of breast-feeding is what reduces the risk. What if women who breast-fed their children are just more health conscious overall throughout life? What if they exercise more often, or have healthier diets?

A more correct headline would be “Breast-Feeding May Benefit Mothers, Study Suggests”. Indeed, the article itself goes on to say that some experts are cautioning that an association (between breast-feeding and health benefits) does not prove a causal relationship, and that more research would be needed to determine the exact cause of the effect (lower risk).